Encoding Vertex Position into Vertex Colors
After quickly scraping together some knowledge about Python and Blender I managed to create a very basic script to do what I want (looks horrible but does its job).

import bpy
from mathutils import Color, Vector

my_object = bpy.context.active_object.data
vert_list = my_object.vertices
color_map = my_object.vertex_colors.new()

i = 0
for poly in my_object.polygons:
    for idx in poly.loop_indices:
        loop = my_object.loops[idx]
        v = loop.vertex_index
        x = (vert_list[v].co.x + 1) / 2
        y = (vert_list[v].co.y + 1) / 2
        z = (vert_list[v].co.z + 1) / 2

        color_map.data[i].color = Color((x, y, z))
        i += 1